Pricing of guarantee fee reasonable is the key to solve the problem of small and medium-sized enterprises credit. This paper considers the influence of the macro-economic and the micro-factors to the Credit Metrics Model. Then adjust the credit transfer matrix of the enterprise after loan from the bank in order to measure the credit risk of the enterprise and the loss of the guarantee company dynamically. It also gives the method of dynamic pricing .Through the empirical analysis, explaining that the rate of guarantee fee from this method is more reasonable than current using.